1. Field of the Invention
The present invention relates to an image processing apparatus and method in which encoded image data are reduced to an appropriate resolution in high speed when the image data are decoded for display or the like.
2. Description of the Related Art
Recently, digital cameras and other imaging devices have evolved to be able to readily obtain mega pixel size images, and the image data of such images are distributed in large amounts on the Internet and the like. It has been a problem that it takes a prolonged time for processing such large image data when displaying, generating, or distributing them. As such, various methods and systems for processing image data in higher speed are proposed.
For example, U.S. Patent Application Publication No. 20040105119 discloses a relay station that performs image processing on an image obtained by a communication device's camera, such as a cell phone or the like and sent to a receiver by attaching it to an e-mail, thereby the resolution of the image and the like are adjusted according to the specifications of the communication device's camera of the receiver. In this way, the patent publication described above proposes a method for minimizing image quality variations arising from the difference in the capabilities between the cameras of the sender and receiver by processing the image data using the devices provided in the relay station.
As the standard image data format, JPEG and MPEG are often used for still images and moving pictures respectively. In the JPEG and MPEG formats, image data are compressed by an orthogonal transformation, such as a discrete cosine transform (DCT). When image data are decoded, the processing speed of a series of processes from “decoding” to “reduction” may be increased by performing a part of the reduction process during an inverse orthogonal transformation, such as an inverse DCT.
For example, Japanese Unexamined Patent Publication No. 2003-032482 proposes a method in which JPEG compressed image data are transformed by an inverse DCT after data in the frequency domain are selected according to a specified reduction ratio.
In the method described above, reduction of N/8 (N=1 to 7) is achieved by combining the filtering, which is to be performed in the reduction process, with the inverse orthogonal transformation. Thus, the accuracy of the reduced image data is degraded even if the processing speed is increased, or a sufficiently high processing speed is not yet achieved.
Therefore, it is an object of the present invention to provide an image processing method and apparatus capable of decoding and reducing image data in higher speed using any reduction ratio without degrading the accuracy of the reduced image data by eliminating the problems described above.